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opto isolated h bridge PCB design

Discussion in 'Circuit Simulation & PCB Design' started by ardv, Jan 9, 2018.

  1. Pommie

    Pommie Well-Known Member Most Helpful Member

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    With that circuit, the options seem to be full speed either way or brake - I.E. motor shorted.

    Also, isn't 10k a little high as it has to charge the bottom gates when the opto is off.

    Mike.
     
  2. Ian Rogers

    Ian Rogers Super Moderator Most Helpful Member

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    When one side is on, the motor turns one way... When the other is on, the motor turns the other.. If when they are both on it free wheels, then PWM may work... If when they are both on the motor brakes ( stops quick ) then PWM wont work..
     
  3. ardv

    ardv New Member

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    I tried the last circuit
    When giving: high low low the motor turns in the first direction
    When sending: low low high the motor turns in the other direction
    But the speed of the motor is very low, i measured the voltage and found it less then 1 volt.
     
  4. dave

    Dave New Member

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  5. ardv

    ardv New Member

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    this is the circuit i have now
    when i try simulating it with Proteus (adding and Arduino UNO in place of inputs, and a motor in output) i get this errors:
    [SPICE] transient GMIN stepping at time=2.54501e-005
    [SPICE] TRAN: Timestep too small; timestep = 1.25e-019: trouble with node #00000.

    and i'm still having the problem of low voltage, i tried both with 5v and 9v in source bit i get always low than 1v.
     

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  6. Ian Rogers

    Ian Rogers Super Moderator Most Helpful Member

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    In your schematic, Q2 and Q4 are upside down..
     
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  7. ardv

    ardv New Member

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    that was the problem!
    thank you very much
    the circuit is now working

    what about pwm?
    i just add it like the 1st circuit?
    and when i should use it (with low low low ?)
     

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  8. Ian Rogers

    Ian Rogers Super Moderator Most Helpful Member

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    How much current is the motor taking... The original circuit had a PWM controlled ground.... That means another optocoupler..

    To check if you can use PWM on the inputs.... Take both optocouplers high ( high low high ) and see if you can turn the motor by hand easy.. If not it's on brake... Then try low low low and see if you can turn the motor by hand...

    Or the way the original should have been.
    upload_2018-1-13_20-43-23.png
     
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